<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div class="box">我是一个盒子</div>
    <script>
        const box = document.querySelector('.box')
        box.innerHTML = '<strong>更换并加粗</strong>'
        //box.innerText = '<strong>更换并加粗</strong>'
    </script>
</body>
</html>